Currently, high speed reduction rotating power devices are generally classified into worm speed reducers and differential planetary gear speed reducers. With a simple structure, a worm speed reducer is easy to manufacture. But it has problems such as friction-induced wearing and heating, low efficiency, and less durability, which limits the scope of its use. A differential planetary speed reducer uses a profile shifted gear of which an amount of addendum modification (or addendum modification coefficient) is adjusted, which causes problems associated with noise, wear, and durability and it is difficult to manufacture the differential planetary speed reducer.
<Note: See glossary for an amount of addendum modification and addendum modification coefficient>